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The Gas Laws

The Gas Laws. The density of a gas decreases as its temperature increases. Ideal Gas Law. PV = nRT. Brings together gas properties. Can be derived from experiment and theory . Ideal Gas Law.

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The Gas Laws

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  1. The Gas Laws The density of a gas decreases as its temperature increases.

  2. Ideal Gas Law PV = nRT Brings together gas properties. Can be derived from experiment and theory.

  3. Ideal Gas Law At the macroscopic level, a complete physical description of a sample of a gas requires four quantities: • 1. Temperature (expressed in K) • 2. Volume (expressed in liters) • 3. Amount (expressed in moles) • 4. Pressure (given in atmospheres) These variables are not independent — if the values of any three of these quantities are known, the fourth can be calculated.

  4. Ideal Gas Equation Universal Gas Constant Volume P V = nRT Pressure Temperature No. of moles R = 0.0821 atm L / mol K R = 8.314 kPa L / mol K Kelter, Carr, Scott, Chemistry A Wolrd of Choices 1999, page 366

  5. PV = nRT Standard Temperature and Pressure (STP) T = 0 oC or 273 K P = 1 atm = 101.3 kPa = 760 mm Hg P = pressure V = volume T = temperature (Kelvin) n = number of moles R = gas constant 1 mol = 22.4 L @ STP Solve for constant (R) PV nT Recall: 1 atm = 101.3 kPa Substitute values: (1 atm) (22.4 L) (1 mole)(273 K) (101.3 kPa) R = 0.0821 atm L mol K = R = 8.31 kPa L mol K ( 1 atm) R = 0.0821 atm L / mol K or R = 8.31 kPa L / mol K

  6. nRT V = P (500 g)(0.0821 atm . L / mol . K)(300oC) = V 740 mm Hg Ideal Gas Law What is the volume that 500 g of iodine will occupy under the conditions: Temp = 300oC and Pressure = 740 mm Hg? Step 1) Write down given information. mass = 500 g iodine T = 300oC P = 740 mm Hg R = 0.0821 atm . L / mol . K Step 2) Equation: PV = nRT Step 3) Solve for variable Step 4) Substitute in numbers and solve V = What MISTAKES did we make in this problem?

  7. What mistakes did we make in this problem? What is the volume that 500 g of iodine will occupy under the conditions: Temp = 300oC and Pressure = 740 mm Hg? Step 1) Write down given information. mass = 500 g iodine Convert mass to gram; recall iodine is diatomic (I2) x mol I2 = 500 g I2(1mol I2 / 254 g I2) n = 1.9685 mol I2 T = 300oC Temperature must be converted to Kelvin T = 300oC + 273 T = 573 K P = 740 mm Hg Pressure needs to have same unit as R; therefore, convert pressure from mm Hg to atm. x atm = 740 mm Hg (1 atm / 760 mm Hg) P = 0.9737 atm R = 0.0821 atm . L / mol . K

  8. nRT V = P (1.9685 mol)(0.0821 atm . L / mol . K)(573 K) = V 0.9737 atm Ideal Gas Law What is the volume that 500 g of iodine will occupy under the conditions: Temp = 300oC and Pressure = 740 mm Hg? Step 1) Write down given information. mass = 500 g iodine n = 1.9685 mol I2 T =573 K (300oC) P =0.9737 atm(740 mm Hg) R = 0.0821 atm. L / mol . K V = ? L Step 2) Equation: PV = nRT Step 3) Solve for variable Step 4) Substitute in numbers and solve V = 95.1 L I2

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